1. Field of the Invention
The present invention relates generally to a dry etching apparatus for manufacturing semiconductor devices, and more particularly, to a dry etching apparatus having an improved dielectric window.
2. Description of the Related Art
Generally, semiconductor devices are manufactured by forming multiple layers such as an insulating layer or a conductive layer on a semiconductor substrate and then patterning the layers. The patterns are formed by photolithography, which typically includes: depositing photoresist on the layers, forming a photoresist pattern by exposure and development, and etching the layers using the photoresist pattern as an etching mask. The etching step may be accomplished with either a wet etching using chemicals or a dry etching using plasma, although dry etching is generally preferred when forming high integration semiconductor devices.
Many devices have conventionally been used to improve the density distribution of plasma in the dry etching chamber. These include using an Electron Cyclotron Resonance (ECR) apparatus, an Inductivity Coupled Plasma (ICP) apparatus, or a Transformer Coupled Plasma (TCP) apparatus. In particular, a typical TCP apparatus is described in U.S. Pat. No. 5,731,565 to Gates. As described by Gates, a Transformer Coupled Plasma (TCP) apparatus includes a process chamber in which the plasma etching process is carried out and a dielectric window covering the upper side of the process chamber and sealing the process chamber. A chuck that holds the wafer to be etched is placed on the lower side of the process chamber. A helical-shaped coil is positioned outside of the process chamber on the upper side of the dielectric window and generates fields that induce plasma to form inside the chamber.
FIGS. 1 and 2 illustrate a conventional dielectric window. Dielectric window 1 is planar shaped, is of a certain thickness, and is made of quartz. The dielectric window 1 protects the inductive coil of the TCP apparatus from plasma inside the process chamber.
One problem associated with dielectric window 1 is that by-products, such as polymers, created during the etching process tend to attach to the lower surface of the dielectric window 1, with a greater portion of the polymers attaching to the center of the dielectric window 1 than to the peripheral portions. This can be detrimental to the etching process, because if the by-products detach during etching, they may contaminate the wafer. This problem can be exacerbated if the plasma unintentionally etches the lower surface of dielectric window 1 and deforms its shape.
One attempt at solving the above discussed problem is described in U.S. Pat. No. 5,401,350 to Patrick et al. This patent describes an inductive coil having more winding turns of the coil in its periphery than in its center. However, by-products still tend to form in greater proportions near the center of the dielectric window than at the periphery.
The by-products form on dielectric window 1 due to unintentional sputtering of the by-products on to the lower surface of the dielectric window 1 by capacitive coupling caused by radio frequency power applied to the inductive coil. As the by-products accumulate on the dielectric window during repeated etching procedures, the likelihood of some of them detaching and contaminating the wafer increases. Moreover, if the dielectric window is unintentionally etched, debris from the etching may also become a source of contamination to the wafer.
In summary, conventional dielectric windows used in dry etching devices suffer several disadvantages, including the fact that by-products of the etching, such as polymers, may accumulate on the dielectric window and the dielectric window itself may be unintentionally etched. These problems are sources of process failures during etching and affect the life time of the dry etching apparatus.